Self-assembly addresses how structures and machines can build themselves. Self-assembly is ubiquitous in nature, from cellular components to dynamically organizing insect colonies. These self-assembly concepts have many applications in engineering, as described, e.g., in R Pfeifer, et al., “Self-Organization, embodiment, and biologically inspired robotics,” 318 Science 1088-1093 (2007); and several artificial methods for self-assembly have been developed at length scales ranging from nanometers to centimeters [see, e.g., G. M. Whitesides, et al., “Self-Assembly at All Scales,” 295 Science 2418-2421 (2002)].
One particularly useful form of self-assembly involves folding two-dimensional materials into three-dimensional structures. Compared to other types of self-assembly, folding offers a capacity for forming complex shapes and can be scaled to different sizes. Folded structures have high strength-to-weight ratios, and planar materials are compatible with a wide range of fabrication techniques (e.g., photolithography). Prior to folding, the integration of system components (e.g., batteries, integrated circuits, motors) can be automated for planar structures with the use of pick-and-place tools used in printed circuit board population.
Several actuation methods for self-folding have been developed at a range of length scales from micrometers to centimeters, including polymer swelling [see J. Guan, et al., “Self-Folding of Three-Dimensional Hydrogel Microstructures,” 109 J. Phys. Chem. 23134-37 (2005)], shape memory materials [see E. Hawkes, et al., “Programmable Matter by Folding,” 107 Proc. Natl. Acad. Sci. USA 12441-45 (2010), and Y. Liu, et al., “Self-Folding of Polymer Sheets Using Local Light Absorption,” 8 Soft Matter 1764-69 (2012)], and magnetic fields [see Y. W. Li, et al., “Magnetic Actuation of Hinged Microstructures,” 8 J. Microelectromech. S. 10-17 (1999)].
Fold patterns can be created using existing computational origami design automation tools [see E. D. Demaine, et al., “Folding Flat Silhouettes and Wrapping Polyhedral Packages: New Results in Computational Origami,” 16 Comput. Geom. 3-21 (2000); G. Song, et al., “A Motion-Planning Approach to Folding: From Paper Craft to Protein Folding,” 20 IEEE Trans. Robot. Autom. 60-71 (2000); T. Tachi, “Origamizing Polyhedral Surfaces,” 16 IEEE Trans. Vis. Comput. Graphics 298-311 (2010); D. M. Aukes and R. J. Wood, “PopupCAD: A New Design Tool for Developing Self-Folding Devices,” presented at the 2014 Materials Research Society Spring Meeting, San Francisco, Calif. 21-25 (April 2014); and B. An, et al, “An End-to-End Approach to Making Self-Folded 3D Surface Shapes by Uniform Heating,” 2014 IEEE International Conference on Robotics and Automation, Hong Kong, China (31 May-7 Jun. 2013)], and many geometries and mechanisms have been invented that harness the unique strengths of folded structures [see H. Okuzaki, et al, “A Biomorphic Origami Actuator Fabricated by Folding a Conducting Paper,” 127 J. Phys. Conf. Ser. 012001 (2008); P. Birkmeyer, et al., “DASH: A dynamic 16 g Hexapedal Robot,” 2009 IEEE International Conference on Intelligent Robots and Systems, St. Louis, USA, 2683-2689 (11-15 Oct. 2009); and H. C. Greenberg, et al., “Identifying Links Between Origami and Compliant Mechanisms,” 2 Mech. Sci. 217-225 (2011)].
Existing approaches to self-folding are capable of creating static geometric structures but may be limited in making complex geometries or functional mechanisms (i.e., structures that move or compute). Functional folded mechanisms have been demonstrated, though they may require manual assembly steps, such as scaffold removal or integration of components after folding [see P. S. Sreetharan, et al., “Monolithic Fabrication of Millimeter-Scale Machines,” 22 J. Micromech Microeng. 055027 (2012), and S. M. Felton, et al., “Robot Self-Assembly by Folding: a Printed Inchworm Robot,” 2013 IEEE International Conference on Robotics and Automation, Karlsruhe, Germany, 277-282 (6-10 May 2013)].